Exposure to pyrethroid insecticides is a growing health concern due to the ban on residential use of organophosphate (OP) insecticides. Pyrethroids have replaced OP for residential pest control. Use is increasing across the U.S. and is particularly high in New York City (NYC). Experimental and preliminary epidemiologic data suggest that prenatal exposure may adversely affect child mental, motor and behavioral development. However, additionally research is urgently needed. The goals of this study are to examine whether biomarkers of prenatal exposure to pyrethroid insecticides are associated with adverse children's cognitive, motor and behavioral development. In doing so, we will also validate a urinary biomarker of prenatal exposure to these compounds for use in epidemiologic research. To accomplish this, we use data from two ongoing longitudinal birth cohorts which together comprise n=325 NYC mothers and children. Pyrethroid metabolites will be measured in urine samples collected and stored from all women during pregnancy. Between child ages 48-58 months, families will be invited to our clinic for development assessments. Cognitive development will be assessed using the Wechsler Preschool and Primary Scale of Intelligence-3rd edition; motor development using the Bruininks-OseretskyTest of Motor Proficiency, 2nd edition; and executive function using the Behavior Rating Inventory of Executive Function-Preschool Version. A home visit will be made to obtain data on the childrearing environment. Child blood samples will be collected to measure lead in whole blood. Questionnaires will be administered to the mother updating social and demographic information, smoking history, and maternal satisfaction and demoralization (the Psychiatric Epidemiology Research Instrument Demoralization Scale) and to gather data on pesticide use. Maternal intelligence will also be assessed (the Test of Non-Verbal Intelligence, 3rd edition). GIS mapping will be used to model neighborhood level SES and other characteristics which may act as a confounder in the current study. Multiple linear regression analysis will be used to examine associations between the pyrethroid metabolites and outcomes, adjusting for potential confounders and multiple comparisons. Results from this study will have immediate public health importance and will inform future studies examining pyrethroid toxicities. Indoor uses of pyrethroid insecticides have been increasing dramatically. Preliminary data suggest that prenatal pyrethroids exposure can adversely affects child learning and behavior. However, no prior study has evaluated associations between pyrethroid metabolites in maternal prenatal urine and cognitive, motor or behavioral outcomes in children.